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from right t left, which enables it to press, cut, and tear the leaves in every direction. Along the whole length of its back we perceive through its skin a vessel which performs the functions of a heart. On each side of this insect are nine orifices, which answer to as many lungs, and assist the circulation of the chyle, or nutritive juice. Under the mouth it has a kind of reel with two holes, through which pass two drops of the gum with which its bag is filled; they act like two distaffs, continually furnishing it with the materials of which it makes its silk. The gum which distils through the two holes takes their form, lengthens into a double thread, which suddenly loses the fluidity of the liquid gum, and acquires the consistence necessary to support or to envelope the worm. When that time arrives, it joins the two threads together, by gluing them one over the other with its fore feet. This double thread is not only very fine, but also very strong, and of great length. Each bag has a thread which is nearly five hundred ells long; and as this thread is double, and joined together throughout its length, each bag will be found to contain a thousand ells of silk, though the whole weight does not exceed two grains and a half.

The life of this insect in its vermiform state is very short, and it passes through different states till it gradually arrives at its greatest degree of perfection. When it first emerges from the egg, it is extremely small, perfectly black, and its head of a still brighter black than the rest of its body in a few days it begins to grow white, or of an ash colour; its coat becomes dirty and ruffled; it casts it off, and appears in a new dress; it becomes larger and much whiter, though a little tinged with green, from feeding upon green leaves. After a few more days (the length of time varying according to the degree of heat and quality of its nourishment) it ceases to eat, and sleeps for about two days; it then agitates and frets itself extremely, becoming red with the efforts it makes; its skin wrinkles and shrivels up, and it throws it off a second time, together with its feet. Within the space of three weeks ɔr a month, we see it fresh dressed three times. It now begins to eat again, and might be taken for a different creature, so much is the appearance of its head, colour, and figure, altered. After continuing to eat for some days, it falls again into a lethargic state; on recovering from which, it once more changes its coat, which makes the third since it issued from its shell. It continues to eat for some time, then, entirely ceasing to take any nutriment, prepares for itself a retreat, ard draws out a silken thread, which it wraps round its body in the same manner as we might wind thread round an oval 1 piece of wood. It remains quietly in the bag it has formed, and at the end of fifteen days would pierce it, to issue forth,

if it was not killed by being exposed to the heat of the sun, or shut up in an oven. The silk-bags are thrown into hot water, and stirred about with birch twigs to draw out the heads or beginning of the threads, and the silk is afterwards wound upon reels made for the purpose. Thus we are indebted to this little insect for our greatest luxury in clothing: a reflection which ought to humble our pride; for how can we be vain of the silk which covers us, when we reflect tc what we are indebted for it, and how little we are instrumental in the formation of those beauties in our clothing, of which we are vain? Thus we find the most insignificant and despicable objects are the instruments of ornament and advantage to man; an insect that we scarcely condescended to look at, becomes a blessing to thousands of human beings, forms an important article of trade, and is the source of great riches.

Our next subject is, THE TAPE-WORM.-This genus of worms is destined to feed on the juices of various animals, and they inhabit the internal parts of almost every species of living beings. The structure and physiology of the tænia are curious, and it may be amusing as well as instructive to consider it with attention. The tænia appears destined to feed upon such juices of animals as are already animalized; and it is therefore most commonly found in the alimentary canal, and in the upper part, where there is the greatest abundance of chyle, for chyle seems to be the natural food of the tænia. As it is thus supported by food which is already digested, it is destitute of the complicated organs of digestion. As the tænia solium is most frequent in this country, it may be proper to describe it more particularly.

It is from three to thirty feet long; some say sixty feet. It is composed of a head, in which are a mouth adapted to drink up fluids, and an apparatus for giving the head a fixed situation. The body is composed of a great number of distinct pieces articulated together, each joint having an organ by which it attaches itself to the neighbouring part of the inner court of the intestine. The joints nearest the head are always small, and they become gradually enlarged as they are farther removed from it; but towards the tail a few of the last joints again become diminished in size. The extremity of the body is terminated by a small semicircular joint, which has no opening in it.

The head of this animal is composed of the same kind of materials as the other parts of its body; it has a rounded opening at its extremity, which is considered to be its mouth. This opening is continued by a short duct into two canals; these canals pass round every joint of the animal's body, and

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-Development of Tenia (from Leuckart). A, Cysticercus bovis in beef; nat. size. B, invaginated head of a Cysticercus before the formation of the Buckers; x 25. C, invaginated head of Cysticercus cellulose, showing the bent neck and receptacle r; x 80. D, stages in the development of the broodcapsules in Echinococcus: a, the thickening of the parenchyma of the bladder; b, subsequent formation of a cavity in it; c, development of the suckers; d, a capsule with one head inverted into its cavity; e, a capsule with two heads; x 90.



5.-Tetrarhynchus. A, General view of the worm; x 4. B, head showing the suckers, proboscides, and excretory canals; x 25. C, portion of a proboscis showing the two forms of hooks; highly magnited. (All from Pintner,)

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-Various Forms of Tape-Worms. A, Tania echinococcus; x 12 (from Leuckart). B, Archigetes sieboldi; x 60 (from Leuckart). C, Echinobothrium typus; x 10 (from Van Beneden). P, Caryophylleus mutabilis; x about 5 (from Carus).

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-Bothriocephalidae. A, A segment of Bothriocephalus latus, showing the generative organs from the ventral surface; ex., excretory vessels; c, cirrus; c.p., cirrus pouch; v.d., vas deferens; v.o., vaginal opening; v, vagina; sh.g., shell-gland; od., oviduct; ov., ovary; y.g., yolk-gland; y.d., its duct; ut., uterus; a.o., uterine opening; the testes are not visible from this side; x 23 (from Sommer and Landois). B, C, marginal and lateral views of the anterior part of B. cordatus, showing the cephalic grooves; x 5 (from Leuckart). D, Ciliated embryo of B. latus; x 60 (from Leuckart).

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